Stabilization of lubricants



United States Patent 3,0935% STABILIZATION OF LUBRICANTS Henryk A. Cyba,Chicago, Ill., assignor to Universal Oil Products Company, Des Piaines,11]., a corporation of Delaware N0 Drawing. Filed Aug. 11, 1960, Ser.No. 48,814

3 Claims. (Cl. 252-515) This is a continuation-in-part of my copendingapplication Serial No. 826,408, filed July 13, 1959, and relates to thestabilization of lubricants and more particularly to a synergisticinhibitor composition and the use thereof in lubricants.

In recent years, stringent requirements for lubricants in certainapplications have resulted in the availability of a new class oflubricants referred to in the art as synthetic lubricants. Theselubricants do not necessarily replace petroleum oils in conventionalusage, but are designed for special applications where the petroleumoils do not function to a satisfactory degree. These syntheticlubricants have found particular use in winter-grade crankcase oils,turbo-engine oils, aviation instruments, automatic Weapons, etc. Forexample, aircraft gas turbines require oils capable of providingsatisfactory lubrication at temperatures ranging as low as 65 F. and ashigh as 275 -F. during use. Temperatures up to 500 F. are encounteredfor intervals of from one to two hours during shut-down. Petroleumlubricants are unsatisfactory at high altitudes or in the winter seasonfor use in machine guns and automatic cannons which frequently could notbe made to fire because of congealed lubricants. Because they are useunder such stringent conditions, the synthetic lubricants may undergoundesirable deterioration including, for example, formation of deposits,discoloration, change of viscosity, etc. While the features of thepresent invention are particularly applicable to the stabilization ofsynthetic lubricants, it is understood that they also may be used forthe stabilization of petroleum lubricants.

The synthetic lubricants are of varied types including aliphatic esters,polyalkylene oxides, silicones, esters of phosphoric and silicic acids,highly fluorinesubstituted hydrocarbons, etc. Of the aliphatic esters,di-(Z-ethylhexyl) sebacate is being used on a comparatively largecommercial scale. Other aliphatic esters include dialkyl azelates,dialkyl suberates, dialkyl pimelates, dialkyl adipates, dialkylglutarates, etc. Specific examples of these esters include dihexylazelate, di-(Z-ethylhexyl) azelate, di-3,5,5-trimethylhexyl glutarate,di-3,5,5-trimethylpentyl glutarate, di-(Z-ethylhexyl) pimelate,di-(Z-ethylhexyl) adipate, triamyl tricarballylate, pentaerythritoltetracaproate, dipropylene glycol dipelargonate,1,5-pentanedioldi-(Z-ethylhexanonate), etc. The polyalkylene oxidesinclude polyisopropylene oxide, polyisopropylene oxide diether,polyisopropylene oxide diester, etc. The silicones include methylsilicone, methylphenyl silicone, etc., and the silicates include, forexample, tetraisooctyl silicate, etc. The highly fluorinatedhydrocarbons include fluorinated oil, perfiuorohydrocarbons, etc.

Additional synthetic lubricating oils include 1) neopentyl glycolesters, in which the ester group contains from 3 to 12 carbon atoms ormore, and particularly neopentyl glycol p *opionates, neopentyl glycolbutyrates, neopentyl glycol ca,.:oates, neopentyl glycol caprylates,neopentyl glycol pelargon-ates, etc., (2) trimethylol alkanes such astrimethylol ethane, trimethylol propane, trimethylol butane, trimethylolpentane, trimethylol hexane, trimethylol heptane, trimethylol octane,trimethyl decane, trimethylol, undecane, trimethylol dodecane, etc., aswell as the esters thereof and particularly triesters in which the esterportions each contain from 3 to 10.

carbon atoms and may be selected from those hereinbetore specificallyset forth in connection with the discussion of the neopentyl glycolesters, and (3) tricresylphosphate, trioctylphosphate,trinonylphosphate, tn'decylphosphate, as well as mixed aryl and alkylphosphates, etc.

The lubricating oils of petroleum origin include those referred to asmotorlubricating oil, railroad type lubricating oil, marine oil,transformer oil, turbine oil, transmission oil, differential oil, diesellubricating oil, gear oil, cutting oil, rolling oil, cylinder oil,hydraulic oil, slushing oil, specialty products oil, etc.

The present invention also is applicable to the stabilization of greasesmade by compositing metallic soaps with the synthetic lubricating oilsdescribed above and are referred to herein as synthetic greases. Thesemetal base synthetic greases may be further classified as lithium basesynthetic grease, sodium base synthetic grease, calcium base syntheticgrease, barium base synthetic grease, strontium base synthetic grease,aluminum base synthetic grease, etc. These greases are solid orsemi-solid gels and, in general, are prepared by the addition to thesynthetic lubricating oil of hydrocarbon-soluble metal soaps or salts ofhigher fatty acids as, for example, lithium stear-ate, calcium stearate,aluminum naphthenate, etc. The grease may contain thickening agents suchas silica, carbon black, talc, organic modified bentonite, etc.,polyacrylates, amides, polyarnides, aryl u-reas, methyl N-noctadecylterephthalamate, etc. Another type of grease is prepared from oxidizedpetroleum wax, to which the saponifiable base is combined with theproper amount of the desired saponifying agent, and the resultantmixture processed to produce a grease. Other types of greases in whichthe features of the present invention are usable include petroleumgrease, whale grease, wool grease, etc., and those made from inediblefats, tallow, butchers waste, etc.

It is general practice to incorporate an antioxidant in syntheticlubricants in order to improve the stability thereof. Research continuesto search for even better inhibitors in order to further improve thesynthetic lubricants and permit their use for longer periods of time inpresent applications, as Well as to permit their use under even moresevere conditions as, for example, in the engines of the future whichare being developed to operate at peak efficiency at high altitudes. Itis important that the synthetic lubricant under these conditions isstable, retains its lubricity properties, does not develop depositformation, retains its desirable viscosity, etc.

It now has been found that a synergistic composition of both anantioxidant and certain nitrogen-containing polymers impart to thesynthetic lubricant a considerably improved stability, much greater thanobtained through the use of the antioxidants alone. In fact, thissynergistic effect is surprising because the polymers themselves do notimprove the stability of the synthetic lubricant to any substantialextent. Normally it would be predicted that this mixture would not beany better than the antioxidant alone. Accordingly, it is surprisingthat these great improvements in the stability of the lubricant areobtained through the use of the novel inhibitor mixture of the presentinvention.

In one embodiment the present invention relates to a method ofstabilizing a lubricant which comprises incorporating therein astabilizing concentration, in a synergistic proportion, of anantioxidant selected from the group consisting of diaminodiphenylethers, diamino' diphenyl sulfides and diaminodiphenyl alkanes and asynergist comprising a polymer of two unsaturated compounds, at leastone of which contains a basic nitrogen.

In a specific embodiment the present invention relates to a method ofstabilizing di-(Z-ethylhexyl) sebacate which comprises incorporatingtherein a stabilizing concentration, in a synergistic proportion, of4,4'-di-sec-butyldiaminodiphenyl methane and a polymeric condensationproduct of lauryl methacrylate and beta-diethylaminoethyl methacrylate.

In another specific embodiment the present invention relates to a methodof stabilizing lithium base grease which comprises incorporating thereina stabilizing concentration, in a synergistic proportion, of2,4-di-secbutyl-diaminodiphenyl ether and a polymeric condensationproduct of n-octyl methacrylate and beta-diethylaminoethyl methacrylate.

In another embodiment the present invention relates to a lubricantcontaining a stabilizing concentration of the synergistic inhibitorcomposition herein defined.

As hereinbefore set forth, the antioxidant used in the novel stabilizingcomposition of the present invention is selected from the groupconsisting of diaminodiphenyl ethers, diaminodiphenyl sulfides anddiaminodiphenyl alkanes.

In a preferred embodiment the diaminodiphenyl alkanes contain from 1 to4 carbon atoms in the alkane group and thus include the correspondingmethanes, ethanes, propanes and butanes. Of these the diaminodiphenylmethanes and diaminodiphenyl propanes are particularly preferred. Thepreferred diaminodiphenyl Inethanes include N,N'-diisopropyldiaminodiphenyl methane, N,N'-di-sec-butyl-diaminodiphenyl methane,N,N'-di-sec-amyl-diaminodiphenyl methane,N,N-di-sechexyl-diaminodiphenyl methane,N,N'-di-sec-heptyldiaminodiphenyl methane, N,Ndi-sec-octyl-diaminodiphenyl methane, N,N di-sec-nonyl-diaminodiphenylmethane, N,N-di-sec-decyl-diaminodiphenyl methane,N,N'-di-sec-undecyl-diaminodiphenyl methane,N,N-disec-dodecyl-diaminodiphenyl methane,N,N'-di-sec-tridecyl-diaminodiphenyl methane,N,N-di-sec-tetradecyldiaminodiphenyl methane, etc. Other antioxidantsinclude N,N'-di-cyclohexyl diaminodiphenyl methane and alkylatedderivatives thereof. The amino groups are preferably in the 4,4'- and/or2,4'-positions. It is understood that other suitable diaminodiphenylmethanes may be used in some applications.

Of the diaminodiphenyl propanes, preferred antioxidants includeN,N'-diisopropyl-diaminodiphenyl propane,N,N-di-sec-butyl-diaminodiphenyl propane, N,N-di-secamyl-diaminodiphenylpropane, N,N di sec hexyldiaminodiphenyl propane,N,N-di-sec-heptyl-diaminodiphenyl propane,N,N-di-sec-octyl-diaminodiphenyl propane,N,N'-di-sec-nonyl-diaminodiphenyl propane, N,N'-di-sec-decyl-diaminodiphenyl propane,N,N'-di-sec-undecyl-diaminodiphenyl propane, N,N' di secdodecyldiaminodiphenyl propane, N,N'-di-sec-tridecyl-diaminodiphenylpropane, N,N'-di-sec-tetradecyl-diaminodiphenyl propane, etc. Otherantioxidants include N,N'-dicyclohexyl diaminodiphenyl propane andalkylated derivatives thereof. The amino groups are preferably in the4,4- and/or 2,4'-positions. It is understood that other suitablediaminodiphenyl propanes may be used in some applications.

Any suitable diaminodiphenyl ether may be used as the antioxidantcomponent of the inhibitor composition. Preferred diaminodiphenyl ethersinclude N,N-diisopropyl-diaminodiphenyl ether,N,N-di-sec-butyl-diaminodiphenyl ether, N,N' di-sec-amyl-diaminodiphenylether, N,N'-di-sec-hexyl-diaminodiphenyl ether,N,N-di-secheptyl-diaminodiphenyl ether,N,N'-di-sec-octyl-diaminodiphenyl ether, N,N di sec nonyldiaminodiphenyl ether, N,N-di-sec-decyl-diaminodiphenyl ether,N,N-disec-undecyl-diaminodiphenyl ether, N,N'-di-sec-dodecyldiaminodiphenyl ether, N,N-di-sec-tridecyl-diaminodiphenyl ether, N,N'di-sec-tetradecyl-diaminodiphenyl ether, etc. Other antioxidants includeN,N'-di-cyclohexyl diaminodiphenyl ether and alkylated derivativesthereof. The amino groups are preferably in the 4,4- and/or2,4'-positions.

Any suitable diaminodiphenyl sulfide may be used as the antioxidantcomponent of the inhibitor composition. Preferred diaminodiphenylsulfides include N,N-diisopropyl-diaminodiphenyl sulfide, N,N' disec-butyl-diaminodiphenyl sulfide, N,N'-di-sec-amyl-diaminodiphenylsulfide, N,N-di-sec-hexyl-diaminodiphenyl sulfide, N,N'-di-sec-heptyl-diaminodiphenyl sulfide, N,N'-di-sec-octyldiaminodiphenylsulfide, N,N-di-sec-nonyl-diaminodiphenyl sulfide,N,N'-di-sec-decyl-diaminodiphenyl sulfide,N,N-di-sec-undecyl-diaminodiphenyl sulfideN,N'-di-secdodecyl-diaminodiphenyl sulfide,N,N'-di-sec-tridecyl-diaminodiphenyl sulfide,N,N-di-sec-tetradecyl-diaminodiphenyl sulfide, etc. Other antioxidantsinclude N,N'-dicyclohexyl diaminodiphenyl sulfide and alkylatedderivatives thereof. The amino groups are preferably in the 4,4'- and/or2,4'-positions.

It is understood that the dilferent antioxidants are not necessarilyequivalent, but all will form a synergistic mixture with the polymercontaining a basic nitrogen and will produce improved benefits over andabove those expected from the use of either component separately.

The polymer containing a basic nitrogen for use in the synergisticmixture is produced by the polymeric condensation of an unsaturatedcompound having a polymerizable ethylenic linkage and an unsaturatedcompound having a polymerizable ethylenic linkage and a basic nitrogen.In a preferred embodiment the first-mentioned unsaturated compound isamine free and contains from 8 to 18 carbon atoms in an acyclic chain.Examples of such compounds include saturated and unsaturated long chainesters of unsaturated carboxylic acids such as 2- ethylhexyl acrylate,nonyl acrylate, decyl acrylate, undecyl acrylate, dodecyl acrylate,tridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecylacrylate, heptadecyl acrylate, octadecyl acrylate, etc., andparticularly methacrylates including n-octyl methacrylate, nnonylmethacrylate, 3,5,5-trimethylhexyl methacrylate, n-decyl methacrylate,seccapryl methacrylate, lauryl methacrylate, dodecyl methacrylate,tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate,hexadecyl methacrylate, cetyl methacrylate, heptadecyl methacrylate,octadecyl methacrylate, 9-octadecenyl methacrylate, etc.; unsaturatedesters of long-chain carboxylic acids such as vinyl laurate, vinylstearate; long-chain esters of vinylene dicarboxylic acids such asmethyl lauryl fumarate; long-chain monoolefins such as the alkyl or acylsubstituted styrenes as, for example, dodecyl styrene, and the like. Aparticularly preferred compound is lauryl methacrylate and moreparticularly technical lauryl methacrylate which is obtained byesterification of a commercial mixture of long-chain alcohols in the Cto C range derived from coconut oil. The technical lauryl methacrylateis available commercially at a lower price and, accordingly, ispreferred. A typical technical lauryl methacrylate will contain in theester portion carbon chain lengths of approximately 3% C 61% C 23% CC16, and C18.

Examples of the second mentioned unsaturated compounds (those containinga basic nitrogen) include p- (beta-diethylaminoethyl)-styrene; basicnitrogen-containing heterocycles carrying a polymerizable ethylenicallyunsaturated substituent such as the vinyl pyridines and the vinyl alkylpyridines as, for example, 2-vinyl-5-ethyl pyridine; esters of basicamino alcohols with unsaturated carboxylic acids such as the alkyl andcycloalkyl substituted aminoalkyl and amino cycloalkyl esters of theacrylic and alkacrylic acids as, for example, beta-methaminoethylacrylate, beta-diethylaminoethyl methacrylate, 4-diethylaminocyclohexylmethacrylate, beta-beta-didodecylaminoethyl acrylate, etc.; unsaturatedethers of basic amino alcohols such as the vinyl ethers of such alcoholsas, for example, beta-aminoethyl vinyl ether, beta-diethylaminoethylvinyl ether, etc.; amides of unsaturated carboxylic acids wherein abasic amino substituent is carried on the amide nitrogen such asN-(beta-dimethylaminoethyl) -acrylamide; polymerizable unsaturated basicamines such as diallylamine, and the like.

The above polymeric condensation product is prepared in any suitablemanner and generally by heating the reactants at a temperature of fromabout 100 to about 175 F. for a period of time ranging from two toforty-eight hours or more, preferably in the presence of a catalyst orinitiator such as benzoyl peroxide, tertiary butyl peroxide, azocompounds as alpha, alpha'-azo-diisobutyronitrile, etc. When desired,the polymerization may be effected in the presence of a solvent andparticularly aromatic hydrocarbons, including, for example, benzene,toluene, xylene, cumene, decalin, naphtha, etc. In general thecondensation is effected using the first mentioned and the secondmentioned unsaturated compounds in proportions to produce a copolymercontaining from about 50% to about 95% and preferably from about 70% toabout 90% by weight of the first mentioned compound and from about 5% toabout 50% and preferably from about to about 30% by weight of the secondmentioned compound.

The proportions of antioxidant and synergist may vary over a Wide rangeand thus may range from 0.1 to 4 and preferably from 0.5 to 2 parts byweight of synergist per one part by weight of antioxidant, although insome cases lower or higher proportions may be used. These proportionsare based upon the active ingredient exclusive of solvent. While theantioxidant and synergist may be added separately to the lubricant, itgenerally is preferred to form a suitable mixture of the antioxidant andsynergist and add the mixture to the lubricant. When desired, theantioxidant and synergist may be prepared as a solution in a suitablesolvent, particularly aromatic hydrocarbons and more particularly anaromatic hydrocarbon as hereinbefore set forth, and marketed or used asa single product. Conveniently, the same solvent is used in the finalsolution as used in the preparation of one or both of the antioxidantand synergist. The solution may comprise from about 10% to about 90% andpreferably from about 25% to about 75% by weight of active ingredient.

The inhibitor composition will be used in the substrate in an amountsufficient to obtain the desired stabilization. This stabilizatingconcentration will be within the range of from about 0.001% to about 5%and preferably from about 0.1% to about 3% by weight of the lubricant.The inhibitor composition is added to the lubricant in any suitablemanner and preferably with intimate mixing in order to obtaindistribution of the inhibitor composition in the lubricant. In somecases the inhibitor composition may be added to the lubricant during themanufacture thereof. For example, when used in grease, the inhibitorcomposition may be added to one or more of the components before finalcompositing thereof.

It is understood that the inhibitor composition of the present inventionmay be used along with other additives incorporated in the lubricant.For example, a metal deactivator, dye, viscosity index improver, pourpoint depressant, antifoaming additive, lubricity and extreme pressureadditive, antiscutfiing additive, etc. may be incorporated in thesynthetic lubricant. When desired, the inhibitor composition of thepresent invention may be prepared as a mixture with one or more of theseother additives and incorporated in this manner in the lubricant.

The following examples are introduced to illustrate furtlrer the noveltyand utility of the present invention but not with the intention ofunduly limiting the same.

EXAMPLE I This example illustrates the use of two diaminodiphenylmethanes and a copolymer of lauryl methacrylate and diethylaminoethylmethacrylate. The diaminodiphenyl methanes were prepared as follows:4,4-di-sec-b-utyl-'diaminodiphenyl methane was prepared by the reductivealkylation of 4,4-diaminodiphenyl methane with ethyl methyl ketone at320 F. in the presence of hydrogen and a platinum-containing catalyst.The 4,4-di-sec-butyl-diaminodiphenyl methane was recovered as a viscousoil, having a specific gravity at 60 F. of 0.995, a Universal viscosityat 100 F. of 511.2 second and at 210 F. of 49.1 seconds, and arefractive index at 20 C. of 1.575- 1.577. 4,4-di-cyclohexyldiaminodiphenyl methane was prepared by the reductive alkylation of4,4-diamin'odiphenyl methane with cyclohexanone in substantially thesame manner as described above. The product is recrystallized fromhexane and recovered as crystals having a melting point of 245 F., abasic nitrogen content of 5.50 meq./ g. and a basic molecular weight of363 (theoretical is 362).

The copolymer is prepared by copolymerizing lauryl methacrylate anddiethylaminoethyl methacrylate in concentrations to yield a producthaving by weight of lauryl methacrylate and 20% by weight ofdiethylaminoethyl methacrylate. The polymerization is efiected byheating the reactants at about 140 F. for about eighteen hours, withvigorous stirring in the presence of benzyl peroxide catalyst. Theproduct is recovered as a straw colored, heavy viscous oil of thegeneral proper-ties set forth in Table I.

Table I Viscosity at 210 F., SSU -2200.

Density, pounds/ gallon 7.5

Color, N.P.A. 1.

Pour point, F 10 to +10. Flash point (C.O.C.), -F 380.

Fire point (C.O.C.), F 420.

Total acidity 0.0.

Total base number, mg. KOH/ g. 8.0 (0.14 meq./g.). Ash, weight percent0.00.

The diaminodiphenyl methanes alone and a synergistic mixture of thesewith the polymeric condensation product were separately evaluated indiootyl sebacate, marketed under the trade name of Plexol 201. Theevaluation was made in accordance with an Oxygen Stability Test, inwhich a cc. sample of the synthetic lubricating oil is placed in a bathmaintained at 400 F. and air is blow therethrough at a rate of 5 litersof air per hour. The sample of synthetic lubricating oil is examinedperiodically and the time to reach an acid number of 5 is reported. Itis apparent that the longer the time required to reach an acid number of5 the more stable is the sample of synthetic lubricating oil. In otherwords, it takes longer for the more stable oil to deteriorate.

The results of these evaluations, along with an evaluation of a sampleof the lubricating oil without additive, are reported in the followingtable:

Table II Sample Hours to No. acid number 01'5 Additive 1 None 91%b3ggvcight of 4,4-di-sec-butyl-diaminodiphenyl m anc.

1% by weight of 4,4-dl-see-butyl-diaminodiphenyl methane plus 1% byweight of the condensation product of Example I.

1% by weight of 4,4-di-cyclohexyl-diamlnodiphenyl methane.

1% by weight of 4,4-di-cyclohoxyl-diaminodiphenyl methane plus 0.5% byweight of the polymeric condensation product of Example I.

1% by weight of 4,4-di-cyclohexyl diaminodiphenyl methane plus 1% byweight of the polymerlc condensation product of Example I.

From the :data in the above table, it will be noted that the synergisticmixture served to increase the time to acid number of 5. In sample No.5, 0.5% by weight of the synergist was used and this served to increasethe time to acid number of 5 from 48 to 75 hours. Sample 6 reports theresults when using 1% by weight of the synergist.

EXAMPLE II As hereinbefore set forth, the improved results obtained byusing the mixture of the present invention is surprising because thepolymeric condensation product itself is not an inhibitor. This is shownby the data in the following table, which were obtained in the samemanner as described in Example I. For comparative purposes, sample No. 1(control sample without additive) is repeated in the following table:

Table III Sample Hours to N Additive acid number of 5 1 None 9 7 1% byweight of the polymeric condensation 10 product of Example I.

From the above data, it will be seen that the polymeric condensationproduct itself was not effective to extend the time required to reach anacid number of 5.

EXAMPLE III than 50 hours.

EXAMPLE IV As hereinbefore set forth, a synthetic lubricant beingconsidered for use at high temperature is pentaerythrit ol ester. Thepen taerythritol ester used in this example is available commerciallyfrom Hercules Powder Company as Hercofiex 600 and is stated to bemonomeric pentaerythritol ester having an acid number of 0.10 maximum, asaponification number of 410, a refractive index at 20 C. of 1.453 and aspecific gravity at 25/25 C. of 0.997.

The evaluations in the pentaerythritol ester are made in substantiallythe same manner as described in Example I for dioctyl sebacate. Thesynergistic inhibitor mixture of this example is 1% by weight of4,4'-di-sec-butyl-diaminodiphenyl propane and 1% by weight of thepolymeric condensation product formed by reacting n-octyl methacrylateand diethylaminoethyl methacrylate. The polymeric condensation productis prepared in substantially the same manner as described in Example I.

A sample of the pentaerythritol ester, when evaluated in this manner,reaches an acid number of 5 witln'n 16 hours. The use of the synergisticmixture described above increases the time to reach an acid number of 5in excess of that obtained when using the diaminodiphenyl propane alone,and thereby serves to improve the stability of the lubricant beyond thatexpected when using each of these components alone.

EXAMPLE V Another advantage of the synergistic mixture of the presentinvention is that it also considerably reduces sludge and varnishformation when used in lubricating oil as a result of inhibitingdeterioration of the lubricating oil during use. The following datareports results in a Chevrolet L4 test. This test is run using an enginespeed of 3150 r.-p.m., an engine load of 30 B.H.P., a jacket outlettemperature of 210 F., a jacket inlet temperature of 190 R, an oiltemperature of 280 F. and an air fuel ratio of 14.5:1. Regular gradegasoline and Mid-Continent sol- 8 vent refined S.A.E. 20 typelubricating oil are used. Each run is continued for 36 hours.

The following table reports the results of three runs conducted in theabove manner. In the first run (run A) no additive was incorporated inthe lubricating oil. In the second run (run B) 0.5% by weight of4,4'-di-secbutyl-diaminodiphenyl methane was incorporated in thelubricating oil. In the third run (run C) a synergistic mixture of 0.5by weight of 4,4'-di-sec-butyl-diaminodiphenyl methane and 1% by weightof the polymeric condensation product of Example I were incorporated inthe lubricating oil.

Pertinent data of these runs are reported in the following table:

1 Run was discontinued after 12 hours due to excessive noise.

From the above table it will be seen that, while the use of4,4-di-scc-butyl-diaminodiphenyl methane considerably improved operationof the engine, the use of the synergistic mixture even further improvedthe operation of the engine. It is particularly noteworthy that thevarnish and sludge were considerably reduced. This is further shown bythe considerable reduction in the insoluble matter of the used oil.Also, it will be noted that the viscosity of the used oil containing thesynergistic mixture was lower, thus further indicating inhibition ofdeterioration of the lubricating oil during use.

EXAMPLE VI The synergistic mixture of this example is 0.5 by weight of amixture of 70% by Weight of 2,4-di-secbutyl-diaminodiphenyl ether and30% by weight of 4,4- di-sec-butyl-diaminodiphenyl ether and 1% byweight of the polymeric condensation product of Example I.

The present runs were made in the Chevrolet L4 test in substantially thesame manner as described in Example V. Pertinent results are reported inthe following table:

Table V Run D Run E Run F Diamino- Synergistic No additive diphenylmixture ether Total varnish and sludge, gravimetric, grams 7. 289 1. 767

At 8 hrs. At 36 hrs. At 36 hrs.

Used oil analyses:

Pentane insolubles, weight percent 0. 0449 0. 786 0. 376 Benzeneinsolubles, weight percent 0. 237 0. 541 0. 242 Insoluble resin, weightper- 0.212 0.245 0.134 Viscosity, S.S.U. at F. 608 358 354 1 Run wasdiscontinued after 12 hours due to excessive noise.

Here again it will be noted that the synergistic mixture served toimprove the operation of the engine as compared to the use of thediaminodiphenyl ether alone. This is illustrated by the considerablylower sludge "and varnish formation and the insoluble matter of the usedoil, again showing inhibition of deterioration of the lubricating oilduring use.

EXAMPLE VII The synergistic mixture of this example comprised 0.5% byweight of 2,4'-di-sec-butyl-diaminodiphenyl ether and 1% by weight ofthe polymeric condensation product of Example I.

The results of runs made in the same manner as described in Example Vare reported in the following table:

1 Run was discontinued after 12 hours, due to excessive noise.

Here again it is seen that the synergistic mixture of the presentinvention considerably improved the operation of the engine andinhibited deterioration of the lubrieating oil during use.

EXAMPLE VIII The synergistic mixture of the present example comprises 1%by weight of 4,4'-di-sec-butyl-diaminodiphenyl propane and 1% by weightof the polymeric condensation product of Example I.

The synergistic mixture is incorporated in dioctyl sebacate in aconcentration of 1% by weight based on the lubricant. The lubricantcontaining the synergistic mixture then is utilized at elevatedtemperature. The lubricant containing the synergistic mixturesatisfactorily performs at the elevated temperature encountered in suchuse.

EXAMPLE IX The synergistic mixture of this example comprises 2% byweight oat 4,4-diisopropyl diaminodiphenyl propane and 1% by weight ofthe polymeric condensation product of n-octyl methacrylate andbeta-methylaminoethyl acrylate. The latter condensation product isformed in substantially the same manner as described in Example I.

The synergistic mixture described above is used in a concentration of 1%by weight in a synthetic lubricant comprising mixed oaproic and caprylicacid esters of trimethylol propane. The lubricant containing thesynthetic mixture is stable for use at elevated temperature and highaltitudes.

I claim as my invention:

1. A synergistic inhibitor composition consisting essentially of onepart by Weight of an antioxidant selected from the group consisting ofN,N'-di-sec-alkyl-and N,N'- di-cyclohexyl-diaminodiphenyl methanes andfrom about 0.1 to about 4 parts by weight of the polymeric condensationproduct of an alkyl methacrylate and an alkylaminoalkyl acrylate.

2. A synergistic inhibitor composition consisting essentially of onepart by weight of N,N'-di-sec-butyl-diarninodiphenyl methane and fromabout 0.1 to about 4 parts by weight of the polymeric condensationproduct, formed at a temperature of from about to about F., of laurylmethacrylate and beta-diethylaminoethyl methacrylate.

3. A synergistic inhibitor composition consisting essentially of onepart by weight of N,N'-diisopropyl-diaminodiphenyl methane and fromabout 0.1 to about 4 parts by weight of the polymeric condensationproduct, formed at a temperature of from about 100" to about 175 F., ofl auryl methacrylate and beta-diethylaminoethyl methacrylate.

4. A synergistic inhibitor composition consisting essentially of onepart by weight of N,N'-di-cyclohexyl-diaminodiphenyl methane and fromabout 0.1 to about 4 parts by weight of the polymeric condensationproduct, formed at a temperature of from about 100 to about 175 F., oflauryl methacrylate and beta-diethylaminoethyl methacrylate.

5. A lubricating composition comprising a major proportion of dioctylsebacate and from about 0.001% to about 5% by weight of the synergisticinhibitor composition of claim 1.

6. A lubricating composition comprising a major proportion of dioctylsebacate and from about 0.001% to about 5% by weight of the synergisticinhibitor composition of claim 2.

7. A lubricating composition comprising a major proportion of dioctylsebacate and from about 0.001% to about 5% by weight of the synergisticinhibitor composition of claim 3.

8. A lubricating composition comprising a major proportion of dioctylsebacate and from about 0.001% to about 5% by weight of the synergisticinhibitor composition of claim 4.

References Cited in the file of this patent UNITED STATES PATENTS2,000,045 Sloan May 7, 1935 2,290,860 Burk et al July 28, 1942 2,367,264Burk et a1 Jan. 16, 1945 2,452,320 Kluge et a1. Oct. 26, 1948 2,666,044Catlin Jan. 12, 1954 2,737,496 Catlin Mar. 6, 1956 2,889,282 Lorensen etal June 2, 1959 2,892,784 Harle et a1 June 30, 1959 2,944,974 Lorensenet a1 July 12, 1960 FOREIGN PATENTS 808,665 Great Britain Feb. 11, 1959

1. A SYNERGISTIC INHIBITOR COMPOSITION CONSISTING ESSENTIALLY OF ONEPART BY WEIGHT OF AN ANTIOXIDANT SELECTED FROM THE GROUP CONSISTING OFN,N''-DI-SEC-ALKYL-AND N,N''DI-CYCLOHEXYL-DIAMINODIPOHENYL METHANES ANDFROM ABOUT 00.1 TO ABOUT 4 PARTS BY WEIGHT OF THE POLYMERIC CONDENSATIONPRODUCT OF AN ALKYL METHACRYLATE AND AN ALKYLAMINOALKYL ACRYLATE.
 5. ALUBRICATING COMPOSITION COMPRISING A MAJOR PROPORTION OF DIOCTYLSEBACATE AND FROM ABOUT 0.001% TO ABOUT 5% BY WEIGHT OF THE SYNERGISTICINHIBITOR COMPOSITION OF CLAIM 1.